Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$55.75	12.186%	$62.5437	$62.54	$62.55	$62.50
Purchase #2	$114.74	4.450%	$119.8459	$119.85	$119.85	$119.80
Purchase #3	$99.93	6.422%	$106.3475	$106.35	$106.35	$106.30
Purchase #4	$40.40	12.342%	$45.3862	$45.39	$45.40	$45.40
Purchase #5	$211.92	7.622%	$228.0725	$228.07	$228.05	$228.10
Purchase #6	$105.49	7.788%	$113.7056	$113.71	$113.70	$113.70
Purchase #7	$114.36	8.152%	$123.6826	$123.68	$123.70	$123.70
7 purchase totals =	$742.59		$799.5840	$799.59	$799.60	$799.50